You are right. This is bad. More than bad, it is criminal. I know this is shocking advice, but it is the only thing that will work. You need to send the police to that house and get them all busted. Only the court system is strong enough to make people like that stop.
You think I don't know what I'm talking about. But I do. My son was addicted to marijuana. He sold it out of our house. I kicked him out of the house. Then he got busted. He was in a drug rehab program for 3 years. He could not even drink a beer. Nothing. They drug tested him almost daily, and put him on antibuse to stop the drinking. And they put him in a 30 day rehab program. Oh yea, and they put him in jail on and off over those 3 years if they even fantasized that he had smoked or drunk something. And it did work. He is a productive member of society now. But nothing short of that would ever work. And lastly, he had to completely change who his friends were. He could not associate with his old friends anymore. Because they were still drug and alcohol abusers. And several of them are dead now.
I really wonder what your H's relationship with the RM is. He chooses him over you and his son. This is not just a RM. This is a weird relationship. Maybe it is just that he is his drug supplier. But maybe it is even more than that. It doesn't matter how long you put SS in a rehab program. If he doesn't change who he associates with he will be using the same day he gets out. They do not change by choice.